A control valve is typically used to control the flow of liquids, gas and steam in a variety of industrial applications including chemical, petrochemical, bio-tech, food and beverage, pharmaceutical, general industrial, and research applications. Control valves may be configured in a variety of different ways to provide precision control for the wide variety of applications. Typical control valve designs range from ¼ to 2 inch flow channels; handle pressures from vacuum to 60,000 PSI; handle temperatures from cryogenic to 1500° F., and control the flow of a wide selection of materials. Although typical control valves are described above, custom control valves can be configured from most any application.
Typical control valves are driven by a pneumatic actuator, referred to herein as a control valve actuator. The control valve actuators control the volume of liquid and/or gas flowing through the control valve based on a control signal received at the actuator. Accordingly, control valves may be controlled to provide greater or lesser flow volumes based on a current demand, based on a desired flow volume, etc.
In operation, control valves may experience a difference between a set flow volume, representing a desired flow volume and the actual flow volume allowed by the control valve. The deviations may be corrected for using control valve positioners.
Control valve positioners are used to avoid the influence of forces such as friction and/or differential pressures that can affect the valve position. These forces typically are created from different pressures in the valve itself.
A control valve positioner relates the input signal indicating a measured flow volume to the valve position representing the desired flow volume, and will provide a signal to the control valve actuator to correct for deviations in the two values. The control valve positioner is usually fitted to a yoke or pillars of the actuator, and it is linked to a spindle of the actuator by a feedback arm in order to monitor the valve position. The control valve positioner measures the actual stroke of the valve and compares it with a set point received from an external device. Depending on the actual stroke and the signal the positioner creates a pneumatic signal to the control valve actuator. Typically, the actual stroke is measured with a lever with a rotating connection to the positioner. Thus, the linear movement of the valve stem is translated to a rotating movement in the positioner.
Typical mounting kits use a spring, either internal or external, to maintain the lever on the control valve stem. However, these springs can induce forces into the valve stem system. Further, erosion of materials in the connection point caused by the constant movement of the valve stem can cause drifting in the position values measured by the control valve positioner.
Accordingly, there remains a need for a control valve positioner mounting that does not introduce additional forces to the valve stem system. There further remains a need for such a mounting that compensates for erosion of materials caused by the constant movement of the valve stem.